The present invention relates to an exposure apparatus and an exposure method, and more particularly to an exposure apparatus used for the photolithography process in a process for fabricating semiconductor devices, liquid crystal displays, thin film magnetic heads, or image pickup devices, and an exposure method applied to the photolithography process.
An exposure apparatus is provided with an illumination optical system for illuminating a circuit pattern formed on a mask such as a photomask or reticle. The image of the circuit pattern is projected onto a substrate such as a wafer or glass plate coated with a photosensitive material through a projection optical system and the circuit pattern is transferred onto the substrate. The following is a description of a semiconductor device exposure apparatus for transferring a circuit pattern on a reticle serving as a mask onto a wafer serving as a substrate.
For this type of exposure apparatus, a step and repeat (full wafer exposure type) process is known. The full wafer exposure type exposure apparatus transfers a circuit pattern on a reticle in one shot to a predetermined shot area partitioned on a wafer. The full wafer exposure type exposure is repeated for each of a plurality of shot areas.
A step and scan (scanning exposure)-mode exposure apparatus is also known. The scanning exposure-mode exposure apparatus scans a circuit pattern on a reticle with exposure light shaped like a slit by moving a reticle at a predetermined speed, for example. At the same time, the circuit pattern on the reticle is transferred to the predetermined shot area on a wafer by moving the wafer synchronously with the reticle. Scanning exposure is stepwise for each of a plurality of shot areas.
It is known that distortion such as strain or deformation occurs on the image due to the external environment (atmospheric pressure or temperature), an operating state of the exposure apparatus or a curve of the image face of the reticle. The distortion includes distortions due to magnification, rotation, skew, and a shape component of a shot area. These distortions are described below by referring to FIG. 9.
A standard pattern image 80 is a normal pattern image free from a distortion. Pattern images 81 and 82 respectively have a distortion due to a magnification of a shot area and the pattern image transferred by a projection optical system is enlarged or reduced in size because the magnification of the pattern image is not normal. A pattern image 83 has a distortion due to rotation and is transferred to a position that is rotated from the standard pattern image 80. A pattern image 84 has a distortion due to skew, such that a parallelogram like pattern image that is diagonally shifted from the standard pattern image 80 is transferred due to a shift of synchronous scanning between a reticle stage and a wafer stage. A pattern image 85 has a distortion due to a circuit pattern shape component, such that an irregularly deformed pattern image is transferred. These distortions can occur independently or together.
The distortion of a pattern image may differ for each shot. However, a conventional exposure apparatus does not properly control or compensate for the distortion generated for each shot. Therefore, when a semiconductor device is fabricated, mask superposition accuracy is lowered. Further, when a distortion different for each exposure apparatus occurs when a plurality of exposure devices are used, superposition accuracy is lowered due to the difference between the distortions, and thus the total overlay is deteriorated.
The present invention overcomes such distortion problems. Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
It is an object of the present invention to provide an exposure apparatus and an exposure method capable of superimposing pattern images with a high accuracy for a shot area on a substrate.
In a first aspect of the present invention, an exposure apparatus for exposing a substrate to a pattern image formed on a mask to transfer the pattern onto the substrate is provided. The apparatus includes a substrate stage on which the substrate is mounted and which is movable together with the substrate when exposing the substrate to the pattern image. A memory device stores distortion information of the pattern image generated in accordance with an exposure position on the substrate when the pattern image is being transferred onto the substrate.
In a second aspect of the present invention, an exposure apparatus for exposing a substrate to a pattern image formed on a mask to transfer the image onto the substrate is provided. The apparatus includes a substrate stage on which the substrate is mounted and which is movable together with the substrate when the substrate is exposed to the image. A compensator compensates for distortion of the pattern image generated in accordance with an exposure position on the substrate when the pattern image is being transferred onto the substrate.
In a third aspect of the invention, a method for exposing a substrate to a pattern image formed on a mask to transfer the pattern onto the substrate is provided. The method includes the steps of obtaining pattern image distortion information generated in accordance with an exposure position on the substrate when the pattern image is being transferred onto the substrate, and exposing the substrate to the pattern image in accordance with the distortion information.